【作者】 祝栋林；

【导师】 孙成；

【作者基本信息】 南京大学 ， 环境科学， 2012， 博士

【摘要】 湖泊等湿地系统是大气甲烷的主要自然释放源。受人类活动的影响,外源营养物质的输入导致湖泊出现不同程度的富营养化。富营养化不仅改变营养物质的循环、引起藻类爆发和沉积物中有机物的累积、还导致厌氧环境的形成及加剧甲烷的释放。我国湖泊大都属于浅水湖泊,目前都遭受到不同程度的富营养化。近年来,我国对这些湖泊进行了综合治理,除削减外源营养物质输入外,还进行了蓝藻打捞及生态清淤等工程。目前对湖泊底泥、水、气介质中甲烷产生及释放整体机制的研究还不清楚,尤其是在上述工程治理的背景下更是缺乏系统的研究。本研究以流域性富营养化浅水湖泊太湖和城市浅水湖泊玄武湖为研究对象,从多角度分析了甲烷的水-气界面交换通量及甲烷在空气、水体及沉积物中的含量,探讨了环境工程手段、水体(沉积物)理化性质和生物因素对水体中甲烷含量和分布的影响,主要包括以下内容：对太湖和玄武湖湖面空气中甲烷浓度进行了分析,发现太湖不同区域空气中甲烷含量的差异性比玄武湖的要大,玄武湖上空甲烷浓度的平均含量比太湖表面空气中甲烷含量要高。太湖清淤区域的甲烷空气浓度要比未清淤区域的显著较低,太湖北部未清淤区域较东南部未清淤区域甲烷空气浓度略高。甲烷在水-气界面的交换通量与季节变化有关,其中冬季和春季的通量低于夏季和秋季。沉积物的分布和厚度对上覆水体中甲烷的垂向分布浓度变化有影响,沉积物含量多的地方呈现梯度效应,且含量通常比无沉积物区的要高。对太湖和玄武湖水体中各项理化指标变化与表层水体中甲烷含量间的关系进行主成分分析,甲烷在太湖上覆水体中与氮组分相关性大,而在玄武湖上覆水体中与磷组分相关性大,说明水体中甲烷的含量变化在两种湖泊中的影响机制有所差异。另外太湖水体的pH、溶解氧、总有机碳和藻类等指标对同一组分具有较大的贡献,并且指标间能够进行合理解释,表明主成分分析法的结果具有较高的可靠性,而甲烷的含量与其他指标的变化间存在差异,表明水体中甲烷的含量受多种因素的影响。本研究对表层沉积物中的甲烷含量及多种理化指标进行了分析,发现两个湖泊的表层沉积物的粒径、pH、总氮和含水率等指标变化不大；主成分分析结果显示两个湖泊中甲烷的含量与其他指标间的关系有一定的差异。对表层沉积物中总氮、氨氮、总磷、正磷酸盐和金属离子如Mn、Zn、Fe、Ni、Cu和Mg等指标进行了主成分分析,发现这些指标中玄武湖表层沉积物间隙水各指标总体分为三个组分,氨、正磷酸盐、镍和甲烷主要在第二组分上、铁和水-气界面间甲烷通量在第三组分上；太湖的各指标中,Mn、Mg和甲烷主要在在第二组分,Ni和水-气界面甲烷通量主要在第三组分。对垂向沉积物中甲烷和理化指标进行了分析,结果表明甲烷浓度在表层(0-6cm)比深层(6-21cm)的明显要低。pH值、TP、TN和OM等指标也随着深度变化有所降低。主成分分析结果显示,玄武湖的水分含量、pH值、总氮和总有机质含量主要在第一组分上,而甲烷和总磷主要在第二组分上；然而太湖的各个指标间均在同一组分上。玄武湖沉积物中过氧化氢酶的活性在表层低于底层,而在太湖沉积物中则表现出先升高后降低的趋势,其底层沉积物的活性显著低于表层；纤维素酶的活性在玄武湖和太湖梅梁湾的沉积物中变化趋势相同,都呈下降趋势；玄武湖沉积物中蔗糖酶的活性在3-6cm处最高,其他层间变化不大,而太湖沉积物中蔗糖酶的活性呈现下降趋势；玄武湖沉积物中脲酶的活性在垂直方向上变化不大,而在太湖沉积物中其活性在垂直方向上在增加,但增加的趋势在统计学上差异不大。玄武湖沉积物中细菌的16S rRNA基因的拷贝数在2.44-15.86x109g-1干重沉积物之内,而太湖梅梁湾的细菌16S rRNA基因的拷贝数在不同沉积物内变化相对较大；玄武湖古细菌的16S rRNA基因拷贝数在4.84-17.71×108之内,而太湖沉积物中古细菌的16S rRNA基因拷贝数变化在0.11×108-17.44×108拷贝数每克沉积物湿重内。甲烷菌甲烷杆菌目Methanobacteriales, MBT),甲烷微菌目Methanomicrobiales, MMB)和甲烷八叠球菌目(Methanosarcinales, MSL)属及甲烷八叠球菌属(Methanosarcinaceae)和甲烷鬃菌科(Methanosaetaceae)种的甲烷菌在玄武湖和太湖沉积物中各层中得到检出,并且MMB和MSL的丰度通常高于MBT的丰度。甲基辅酶M还原酶alpha亚基(mrcA)基因在玄武湖和太湖沉积物中都有分布,但是在玄武湖垂向沉积物的0-3cm处和太湖垂向沉积物的0-6cm处该基因低于检出限。通过利用基因文库构建技术克隆了2个mrcA基因,与Genbank中已有基因具有很高的相似性。拟合估算太湖甲烷释放量为2.28万吨/年,太湖流域主要湖泊甲烷释放量为2.64万吨/年,江苏省主要湖泊甲烷量释放为5.52万吨/年,江苏省淡水水域甲烷释放量为16.3万吨/年：太湖甲烷年释放量占目前已普查全省甲烷释放量的1.8%,全省主要湖泊甲烷年释放量占4.3%,全省淡水水域甲烷释放量占12.75%。太湖生态清淤工程对清淤区域空气甲烷浓度的影响显著,清淤区域比未清淤区域空气甲烷浓度均值浓度削减了23.3%。近五年来太湖流域生态清淤工程从流域湖泊、河道水体中削减甲烷含量约157.36万吨,约占我省2010年甲烷释放量的123%；其中太湖湖体生态清淤工程削减甲烷含量约52.2万吨,对削减流域水体内源甲烷含量,减少江苏省温室气体排放贡献显著。研究工作对将江苏省湖泊水体甲烷释放纳入IPCC温室气体排放清单,核算生态清淤工程对水体内源甲烷含量的削减贡献,引入温室气体减排交易资金,具有前瞻性意义。更多还原

【Abstract】 Wetland systems including lake are one of the important natural sources that release methane into atmosphere. Abundant nutrient release causes the eutrophycation in lakes due to human activities. Eutrophic water column not only induce the imbalance of nutrient cycle, the burst of algae and the accumulation of organic matters in the sediments but also induce the formation of anaerobic environment and enhance the release of methane from lakes to atmosphere. In China, abundant shallow lakes are currently being subject to the varying degrees of eutrophication. Many processes including reduction the loads of exterior nutrient, cyanobacteria salvage and ecological dredging project were considered to improve the quality of water. However, factors about the production and release of methane from sediments to the air remain unclear, particularly in the lake, where the ecological dredging projects are performing.The methane current at water-gas interface and methane concentrations in water column, air and sediments were determined in the Taihu Lake and Xuanwu Lake (located in Nanjing) and the effects of environmental engineering, physico-chemical parameters of water (sediments) and biological parameters on the fate of methane were also discussed.Methane concentration was determined in the atmosphere above the surface water (0.5m) of Taihu Lake and Xuanwu Lake, and it varied more significant among sampling site in that of Taihu Lake than in that of XuanWu Lake and was higher in XuanWu Lake than that in Taihu Lake. The methane fluxes at water-air interface associated with the season and it was lower in winter and spring than that in summer and autumn. The distribution and thickness of sediment and depth of overlying water also affected the vertical distribution of methane concentration in water column, and the methane concentration was higher at regions with thick sediments that those with little sediments.Principal component analysis were performed to analysis the relationships among methane content and many physical and chemical parameters in water column of Xuanwu Lake and Taihu Lake. The results indicated that methane and nitrogen parameters in Taihu Lake showed positive relationship while methane and phosphorus showed positive relationship in Xuanwu Lake, indicating there are different mechanisms affecting the fate of methane in the two lakes. In addition, the pH, DO, TOC and algae parameters were grouped in the same class and can be explained, suggesting the principal component analysis method is reliable to analyze these data and the methane content in water can be affected by many factors as it was revealed that there are difference among the methane content and other parameters.Methane concentration and many physico-chemical parameters were determined in the surface sediments and found that no significant alterations were found among the parameters like partical size, pH, total nitrogen and water content; principal component analysis revealed that there were some differences about the relationship between methane content and other indicators in the surface sediments. Principal component analysis on the level of total nitrogen, and ammonia nitrogen, total phosphorus, phosphate and metal ions like Mn, and Zn, and Fe, and Ni, Cu and Mg in porewater of surface sediment from Xuanwu Lake showed that three main components were generated. Ammonia, phosphate and nickel and methane main weighed on the second components; iron and methane fluxes at water-gas interface weighted on the third components. For Taihu Lake, Mn, Mg and methane weighted mainly on the second components while methane flux at water-air interface and Ni mainly weighted on the third component.Results about the methane content and physic-chemical parameters on the vertical sediments showed that the methane were lower in surface sediment (0-6cm) than that in deeper sediment (6-21cm). The pH values, total phosphorus, total nitrogen and organic matters varied with the increase of depth of sediments. PCA results showed that the water content, pH values, total nitrogen and organic matters weighted mainly on the first component and methane and total phosphorus weighted on the second component for Xuanwu Lake and Taihu Lake, all these parameters weighted on the same component. Catalase activity was lower in the deeper layer of sidiments than that in the surface layer in Xuanwu Lake; while it increased with the depth of sediments and then decreasd thereafter in Taihu Lake. Cellulose activity showed similar trend that decreased with the depth of sediments in both lakes. Sucrase activity reached peak values at3-6cm below surface sediments in Xuanwu Lake and no significant alterations were observed among other layers, while it decreased with the depth of sediments in Taihu Lake. Urease activity detected in the vertical sediments of Xuanwu Lake and increased normally with the increase of depth of sediment in Taihu Lake.Copy number of bacterial16S rRNA gene were2.44-15.86×109g-1fresh weight in sediments of Xuanwu Lake, while it varied significantly in the vertical sediments.16S rRNA gene copy number of archaebacteria was4.84-17.71×108and0.11×108-17.44×108g-1fresh weight in vertical sediments of Xuanwu Lake and Taihu Lake, respectively.Methanogens belonging to MBT (Methanobacteriales), MMB (Methanomicrobiales) and MSL (Methanosarcinales) genus and the Methanosarcinaceae and Methanosaetaceae family were detected in the sediments of Xuanwu Lake and Taihu Lake, and abundance of MMB and MSL are usually higher than that of MBT. MrcA gene was detected in Xuanwu Lake and Taihu Lake, however, it was absent in the vertical sediment of Xuanwu Lake at0-3cm and Taihu lake at0-6cm. Two sequence of MrcA gene were cloned by using mrcA gene library construction technology, and showed a high similarity to the MrcA gene deposited in Genebank.According to fitting evaluation, Taihu methane emissions was22800tons per year, the methane emissions of the Taihu Lake Basin was26400tons per year, and emissions of primary lakes in Jiangsu province methane was55200tons per year. Methane emission of freshwater hydrological basin was163000tons per year. The percentage of the annual methane release volume of Taihu, primary lakes and freshwater hydrological basin are1.8%,4.3%and12.75%, respectively.The influence to methane content in air of the desilting region caused by Taihu ecological dredging project is significantly. Methane content in air of the desilting region is decreased23.3%compared with the content in the air of un-desilting area. In past five years, methane content of Taihu lake basin was cut of about1573600tons from lake, river water by the ecological dredging project, which accounting for about at123%of the total methane release content of Jiangsu province in2010. The co reduction amount caused by ecological dredging project in Taihu lake body is about522000tons, to reduce water endogenous methane content, reduce greenhouse gas emissions in Jiangsu Province outstanding contribution.The results obtained in this study are forward-looking significance for bringing the Jiangsu Province Lake methane release into IPCC greenhouse gas emissions list, for accounting contribution of ecological dredging project to endogenous methane content in water and introduction of greenhouse gas emission trading capital.更多还原